What to Know About Alternate-Day Fasting Schedules

Here are the answers to all your questions about alternate-day fasting schedules. This guide will help you decide which one best fits your lifestyle and goals.

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Understanding an alternate-day fasting schedule

Enter intermittent fasting into any search bar and within seconds, you’ll get about a million results, many of which describe alternate-day fasting, one of the most popular forms of this diet trend.

With alternate-day fasting, you switch off between days of eating and days of fasting. While experts are still debating the value of this approach to weight control, the overall premise and promise of these regimens are the same: Fasting flips your metabolic switch so you start burning fat for fuel instead of the glucose stored in your liver, explains Mark P. Mattson, PhD, adjunct professor of neuroscience at Johns Hopkins University School of Medicine in Baltimore. This spurs weight loss and other health benefits.

Finding an alternate-day fasting schedule that fits into your lifestyle can be a challenge. Luckily, there are several alternate-day fasting schedules that exist. Here’s what you need to know about the schedules, the number of calories you can consume on fasting days, the benefits and drawbacks of each, and how they affect the risk of chronic health conditions, like type 2 diabetes and heart disease.

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Alternate-day fasting

Also known as every-other-day dieting, this modified fast alternates four days of calorie restriction (500 for women, 600 for men) with three days of eating freely. Think of it as feast, fast, feast, fast, and so on, says Krista Varady, PhD, professor of nutrition at the University of Illinois in Chicago, and author of The Every-Other-Day Diet.

The schedule

Sunday: Fast (500 calories for women, 600 for men)

Monday: Healthy eating

Tuesday: Fast (500 calories for women, 600 for men)

Wednesday: Healthy eating

Thursday: Fast (500 calories for women, 600 for men)

Friday: Healthy eating

Saturday: Fast (500 calories for women, 600 for men)

What to eat and drink on fast days

In addition to eating up to 500 or 600 calories on fast days, you can also drink as many zero-calorie beverages as you like. Aim for 50 grams of protein on fasting days plus low-cal veggies—such as a salad with grilled chicken or beans—to feel full longer. A cup of cooked lentils provides about 18 grams of protein, while a roasted chicken breast has 25 grams of protein. As a general rule, protein provides 4 calories per gram.

What to eat and drink on non-fasting days

“On feast days, you can eat whatever you want,” Varady says. The types of food you choose don’t seem to matter as long as your big picture calories are reduced. Despite fasting every other day, most people don’t overdo it on feast days, says Varady, who has done a number of studies on intermittent fasting. “We have shown that people eat only 10 percent more calories than usual on feast days.” Here’s what you need to know about drinking protein shakes while fasting.

Benefits

Alternate-day fasters tend to lose 10 to 15 pounds in three months, which is more than what’s typically seen with other intermittent fasting regimens like time-restricted feeding, which limits eating periods to a certain window of time each day. Varady’s studies have also shown reductions in blood pressure and insulin resistance, a precursor to type 2 diabetes that occurs when your body grows resistant to the effects of the hormone insulin. As a result, blood sugar (or glucose) builds up in your body, where it can cause health problems over time. These fasts may also promote autophagy, a deep cellular clean-up that allows your body to get rid of old, damaged cells and replace them with fresh, new ones, Varady explains.

Drawbacks

Not everyone can hack it. In a study, published in 2017 in JAMA Internal Medicine, 38 percent of the alternate-day fasters dropped out, compared with 29 percent of the regular dieters who restricted calories. “It can be hard to follow for some people,” Varady says. Not everyone likes counting calories every other day. It also takes time to adjust to this way of eating, though alternate-day fasters seem to get control of their hunger within about 10 days, on average, she notes. At that time, most people report feeling energetic on fast days.

The 5:2 Fast

A popular version of alternate-day fasting is known as the 5:2 diet or the fast diet. This modified fast involves two days of calorie restriction (500 for men, 600 for women) and five days of eating freely. You can choose which two days you want to fast.

The schedule

Sunday: Fast (500 calories for women, 600 for men)

Monday: Healthy eating

Tuesday: Healthy eating

Wednesday: Fast (500 calories for women, 600 for men)

Thursday: Healthy eating

Friday: Healthy eating

Saturday: Healthy eating

What to eat and drink on fast days

Choosing high-protein foods can keep you feeling full for longer periods of time. Follow the same 50-gram-per-day rule as you would with alternate-day fasting. Make sure to drink lots of water so you don’t become dehydrated. You can eat one “big” meal late in the day or divvy up the calories among two or three meals, Varady says.

What to eat and drink on non-fasting days

The healthier your choices, the greater the benefits, but it’s not what you eat that matters. Although it makes sense to eat fewer processed foods and more fruits, vegetables, whole grains, and lean proteins, “reducing calories in the long term is what’s important,” Varady says.

Benefits

This version of alternate-day fasting is less extreme, yet the weight loss has been shown to be similar, Varady says.

“If alternate-day fasting is too difficult, 5:2 would be one of the easiest plans to jump into,” says Robin Foroutan, RD, an integrative medicine dietitian at Morrison Center in New York City, and spokesperson for the Academy of Nutrition and Dietetics. The 5:2 plan appears to have similar benefits, as far as overall health, to traditional alternate-day fasting.

In a study, published in 2018 in the British Journal of Nutrition, researchers compared the effects of the 5:2 plan to a calorie restriction diet. Participants who followed the 5:2 diet cleared dangerous blood fats known as triglycerides more efficiently than their counterparts who just cut calories and didn’t fast. High levels of triglycerides are a risk factor for stroke and heart attack. The 5:2 fasters also showed reductions in systolic blood pressure (the pressure in your blood vessels when your heart beats).

Foroutan says this type of alternate-day fast may also encourage autophagy, a process during which your cells remove protein build-up and dead or damaged cell components. And a study, published in 2018 in JAMA Network Open, showed that the 5:2 diet results in weight loss and improved blood sugar control for people with type 2 diabetes. If you have diabetes, always talk to your doctor before starting any type of fast, Foroutan says.

Drawbacks

Like alternate-day fasting, 5:2 may be hard to follow over the long term. You can become dehydrated if you aren’t careful and, initially, you may not feel well on fasting days.

Eat-stop-eat

Based on a popular book by Brad Pilon, the eat-stop-eat approach requires a 24-hour fast once or twice a week. This is essentially extending your overnight fast by 12 hours. With this method, you technically never go a full day without a meal. If you fast from 8 a.m. one day to 8 a.m. the next, you would eat breakfast before 8 a.m. on that first day.

Sunday: Fast from 8 a.m. to 8 a.m. Monday

Monday: Healthy eating

Tuesday: Healthy eating

Wednesday: Healthy eating

Thursday: Fast from 8 a.m. to 8 a.m. Friday

Friday: Healthy eating

Saturday: Healthy eating

What to eat and drink on fast days

You can have as much water or zero-calorie beverages as you like, but that’s all.

What to eat and drink on non-fasting days

As with other alternate-day fasting schedules, you can eat whatever you like on your feast days. Making healthy choices, however, are encouraged.

Benefits

This method is likely easier to comply with than alternate-day fasting and may produce similar benefits in terms of weight loss due to calorie restriction. In addition, it may help fasters flip their metabolic switch so they start burning fat for fuel.

Drawbacks

Like other methods, it can lead to dehydration on fasting days if you aren’t careful. There are currently no studies specifically evaluating Eat-Stop-Eat for weight loss.

36:12

This extreme form of fasting is sometimes called zero-calorie alternate-day fasting, Varady says. It involves switching off between 36 hours of zero-calorie intake with 12 hours of unlimited eating. You eat breakfast when you wake up, then consume any other meals within a 12-hour window after which you fast for 36 hours until the next window.

Sunday: Healthy eating between 8 a.m. and 8 p.m.

Monday: Fast

Tuesday: Healthy eating between 8 a.m. and 8 p.m.

Wednesday: Fast

Thursday: Healthy eating between 8 a.m. and 8 p.m.

Friday: Fast

Saturday: Healthy eating between 8 a.m. and 8 p.m.

What to eat and drink on fast days

You can consume as many zero-calorie beverages as you like on fast days, but that is it. “Drink lots of water to help stave off dehydration,” Foroutan says. Aim for around 64 ounces of water on fasting days. “If you are very thirsty, drink more but be aware of electrolyte imbalances. And ask your doctor if you need to take electrolyte supplements to prevent the consequences of this imbalance, including thirst, headaches, rapid heart rate, and sometimes seizures.”

What to eat and drink on feast days

There are no hard-and-fast rules about what you can or can’t eat on feast days. As with other types of fasts, the healthier your choices, the greater the benefits are likely to be, Foroutan notes.

Benefits

A study, published in 2019 in Cell Metabolism, showed that 36:12 fasters consumed 35 percent fewer calories and lost nearly eight pounds in a month. What’s more, fasters continued to burn fat even on feasting days. When participants could eat normally, they made up for some, but not all of the calories they cut out on fast days.

The fasters also showed decreases in cholesterol, belly fat, and inflammation-related biomarkers. They also showed positive changes in a hormone that may increase lifespan.

Drawbacks

Like other alternate-day fasting methods, the 36:12 diet can lead to dehydration, fatigue, and if you’re prone to it, fainting.

Extended 48- and 72-hour fasting periods

A 48-hour fast is an extended form of intermittent fasting. It involves consuming no calories at all for a full two days and eating a regular diet on the other five. A 72-hour fast is a three-day fast with four days of regular eating. These are technically water fasts and can be risky, Foroutan says.

What to eat and drink on fast days

You can consume as many zero-calorie beverages as you like on fast days. A strict water fast allows only pure water.

What to eat and drink on non-fasting days

Anything goes on feast days, but choosing whole plant-based foods over processed ones is a better choice for overall health and well-being. Consume fresh fruits and vegetables in the two days leading up to a water fast. Once the fast is over, drink juice and gradually reintroduce solid plant-based foods with no added sugar, oil, and salt, says Alan Goldhamer, founder of TrueNorth Health Center, a facility in Santa Rosa, California, that offers in-patient water fasting.

Benefits

You will lose weight because you are cutting calories, Foroutan says. These fasts may also produce some of the changes seen with other alternate-day fasting schedules, but more research is needed. Water fasting about 72 hours before chemotherapy to treat cancer may reduce some of the side effects by protecting normal cells, suggests a study, published in 2016 in BMC Cancer. There is some research that points to benefits associated with high blood pressure, diabetes, epilepsy, and other diseases, says Goldhamer.

Drawbacks

This is extreme and should not be done without medical supervision. If you regularly fast more than 18 hours a day, you are at higher risk of developing painful gallstones and more likely to need surgery to remove your gallbladder. You may feel nauseous and tired during a prolonged water fast. Other potential side effects include headache, back pain, and indigestion. Adhering to a fast can also affect your mood and put a damper on your social life, Foroutan notes.

“There is certainly a therapeutic place for fasting,” she says. “But that doesn’t mean that everyone should do it.”

The bottom line

“The number of choices of alternate-day fasting methods underscores the importance of working with someone to interpret your own body’s response,” Foroutan says. Embarking on an alternate-day fasting plan may not make sense if you’re already under a lot of stress, she adds.

“When you do any type of fast, part of the benefits come from mildly stressing your body; just like when you lift weights, you damage the muscle to make it stronger. With fasting, you are stressing out the body, but it gets stronger in response.”

If you are already stressed, you may not see any benefits.

If you are pregnant or breastfeeding, or have a history of eating disorders, don’t try fasting. Other reasons not to try fasting include:

  • History of diabetes
  • Taking medication that must be taken with food
  • A seizure disorder
  • Operating heavy machinery at your job

Sources
  • Mark P. Mattson, PhD, adjunct professor, neuroscience, Johns Hopkins University School of Medicine, Baltimore
  • Krista Varady, PhD, professor of nutrition, University of Illinois, Chicago
  • U.S. Department of Agriculture: "Chicken and Turkey Nutrition Facts"
  • USDA: "How many calories are in one gram of fat, carbohydrate, or protein?"
  • JAMA Internal Medicine: "Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial"
  • British Journal of Nutrition: "Intermittent v. continuous energy restriction: differential effects on postprandial glucose and lipid metabolism following matched weight loss in overweight/obese participants
  • Robin Foroutan, RD, integrative medicine dietitian, Morrison Center, New York City and spokesperson for the Academy of Nutrition and Dietetics.
  • JAMA Network Open: "Effect of Intermittent Compared With Continuous Energy Restricted Diet on Glycemic Control in Patients With Type 2 Diabetes: A Randomized Noninferiority Trial"
  • Cell Metabolism: "Alternate Day Fasting Improves Physiological and Molecular Markers of Aging in Healthy, Non-obese Humans"
  • Alan Goldhamer, founder of TrueNorth Health Center, a facility in Santa Rosa, California
  • BMC Cancer: "Safety and feasibility of fasting in combination with platinum-based chemotherapy"
  • National Institutes of Health: "To Fast or Not to Fast: Does When You Eat Matter?"

Denise Mann, MS
Denise Mann is a freelance health writer whose articles regularly appear in WebMD, HealthDay, and other consumer health portals. She has received numerous awards, including the Arthritis Foundation's Northeast Region Prize for Online Journalism; the Excellence in Women's Health Research Journalism Award; the Journalistic Achievement Award from the American Society for Aesthetic Plastic Surgery; National Newsmaker of the Year by the Community Anti-Drug Coalitions of America; the Gold Award for Best Service Journalism from the Magazine Association of the Southeast; a Bronze Award from The American Society of Healthcare Publication Editors (for a cover story she wrote in Plastic Surgery Practice magazine); and an honorable mention in the International Osteoporosis Foundation Journalism Awards. She was part of the writing team awarded a 2008 Sigma Delta Chi award for her part in a WebMD series on autism. Her first foray into health reporting was with the Medical Tribune News Service, where her articles appeared regularly in such newspapers as the Detroit Free Press, Chicago Sun-Times, Dallas Morning News, and Los Angeles Daily News. Mann received a graduate degree from the Medill School of Journalism at Northwestern University in Evanston, Ill., and her undergraduate degree from Lehigh University in Bethlehem, Pa. She lives in New York with her husband David; sons Teddy and Evan; and their miniature schnauzer, Perri Winkle Blu.